1. Field of the Invention
The present invention relates to a lens array manufactured by press-molding an molten optical material, a manufacturing method of the lens array, an illuminating optical system and a projector.
2. Description of Related Art
In a typical projector, a light irradiated from an illumination optical device is modulated by an optical modulator according to image information, and then a projection optical device projects the modulated light on a screen in an enlarged manner to display an image.
The illumination optical device is typically provided with a light source, a first lens array, a second lens array, and a superposing lens. A light beam irradiated by the light source is split into a plurality of sub-beams by a plurality of small lenses provided in the first lens array. The plurality of sub-beams pass though the second lens array having a plurality of small lenses corresponding to the plurality of small lenses of the first lens array, and then the sub-beams are superposed on an image formation area of the optical modulator by the superposing lens. With use of such illumination optical device, the intensity of the light irradiating the optical modulator can be uniformly distributed.
As a lens array provided in this type of illumination optical device, a lens array having a highly accurate lens face is disclosed (e.g. Japanese Patent Laid-Open Publication No. 2002-328203).
This lens array includes a base and a dome-shaped lens section that is formed on the base and provided with a plurality of small lenses arranged in a matrix form. In the lens section, lateral faces of outermost small lenses arranged on the outermost periphery thereof are slanted toward the outer edge of the base so as to be angled with respect to one surface of the base.
For manufacturing this type of lens array, a molten optical material is pressed with use of a molding die having a die corresponding to the above lens array. Then, an excess portion formed by the press-working is cut off and thus the lens array is manufactured. During this process, since the molding die has a slant face corresponding to a slant face defining a lateral face of the small lenses, the molten optical material is spread along the slant face when press-molded therein, and the mold face of the molding die is finely copied on the molten optical material. Thus the manufactured lens array has a high-precision lens face.
However, according to the invention disclosed in the above publication, in the production process of the lens array, the excess portion formed by the press-working is cut off, and undesirably the lateral face of the lens array becomes rough because of this cutting. Therefore, if the lens array is held by a holder frame or the like while referring to the lateral face of the lens array as an external position reference face, the lateral face of the lens array should be accurately shaped after cutting the excess portion.
To avoid such troublesome shaping process, the above-mentioned publication discloses a lens array having a press-working face on a part of a cutting face, where the excess portion is cut off. However, manufacturing such lens array requires a molding die with a complex shape as well as a high production accuracy, and thus the production cost of the lens array is increased.
Moreover, according to the invention disclosed in the above publication, the lens array is produced one by one using a molding die in which only one die corresponding to the lens array is formed. Therefore, in the case of manufacturing a plurality of lens arrays, the above invention is disadvantageous in view of the production cost and time.